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What is an enzyme?

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Quick answer

An enzyme is a biological catalyst — usually a protein — that speeds up chemical reactions in living things without being used up. Enzymes make essential reactions, such as digesting food and copying DNA, happen fast enough to sustain life.

Key things to understand

  1. Each enzyme has a specific shape that fits a particular molecule (its substrate), like a lock and key.
  2. They lower the energy needed to start a reaction, so it proceeds far faster.
  3. Enzymes are not consumed — one molecule can catalyze the same reaction over and over.
  4. They work best within specific temperature and pH ranges; extremes can 'denature' (deform) them.
  5. Examples include amylase, which breaks down starch, and DNA polymerase, which copies DNA.

People also ask

What happens if an enzyme is denatured?
Heat or extreme pH can change an enzyme's shape so its substrate no longer fits, and it stops working — one reason a high fever is dangerous.
Are all enzymes proteins?
Almost all are proteins, though a few are RNA molecules called ribozymes. Either way, they speed up specific reactions.
Why is each enzyme so specific?
Its active site has a precise shape and chemistry that fits only certain molecules, so each enzyme catalyzes only its particular reaction.
What do enzymes do?
They dramatically speed up specific chemical reactions in the body without being used up.
How do enzymes work?
Each binds a specific molecule (its 'substrate') at an active site, lowering the energy needed for the reaction.
Why are enzymes important?
Without them, life's reactions (like digestion) would be far too slow to sustain us.

Part of the guide: Food & Kitchen Science →